Electric power substations are part of an electric power system serving a specific geographical area. In a conventional substation, transmission lines, typically within a usual range of 46 kV–500 kV, provide high voltage power. Distribution feeders extend from the substation, in the range of typically 12 kV to 34.5 kV.
A substantial amount of power system protection occurs at the substation, with the protection equipment typically in a control house in the substation yard. The control house will include protective relays and related communication equipment. Various bus lines and bus transfer lines for carrying the high voltage, as well as transformers and bus-tie arrangements, are present at the power substation. Typically, inputs from the various power system equipment, indicating the status thereof, and power flow information, such as the status of various circuit breakers in the substation, are provided over wire connections to the protective relays and related devices within the control house. The protective relays/devices oversee all of the status/power system condition information concerning the various bus lines, transfer lines, transformers and circuit breakers at the substation and provide alarms and circuit breaker trip control signals when such power system equipment is indicated to be outside of specified operating limits.
Alarm signals are also generated by the power system equipment, including alarms from the circuit breakers and the transformers if the condition/operation of the equipment is outside selected limits. This could include, for example, a low pressure alarm from a circuit breaker or a particular physical aspect of a transformer. Other alarms are also possible, even substation yard intrusion alarms. All of this information is provided to the protective relays in the central control house by hardwire connections.
Hence, the control and protection equipment in the control house is responsive to a substantial amount of information, including alarms and other information concerning the operating status of a variety of power system equipment within the substation yard.
Currently, all of the connections from the various power equipment devices are provided by hardwire, i.e. copper, connections, to the individual protective relays in the control house. Each control/protection line requires a separate wire and a separate physical connection to the appropriate relay, i.e. a separate input contact. This arrangement has substantial disadvantages, including expense of the copper wire, relatively long leads, complexity of the overall wiring system and difficulty in the actual wiring, and maintaining the individual wire connections. The complexity and expense of the system typically results in an inability to provide dual, i.e. redundant protection. Failure at any one point in the substation can have significant consequences on the power system, in the absence of a redundant/backup system. Further, the long wire connections provide opportunities for interference from other signals, induction and ground potential rise. Still further, when separate wires extend from one station point, such as a disconnect switch, to a plurality of protection circuit/systems, one or more of the individual connections can fail, leading to that circuit responding incorrectly.
Hence, it would be desirable to have a simpler arrangement which makes less use of hardwire connections while providing fast, convenient, redundant protection which would increase reliability of the protection and control system at a substation